Sound recording and reproducing mechanism



Oct. 18, 1938. B. A. PRocToR 2,133,333

` SOUND RECORDING AND REPRODUCING MECHANISM Filed March 26, 1936 2Sheets-Sheet 1 6 c c4 B INVENTOR 55 54 Bar/0h A. Proctor:

ATTORNEYS.

Oct. 18, 1938. B. A. PRocToR 2,133,333

SOUND RECORDING AND REPRODUCING MECHNISM Filed March 26, 1936 2Sheets-Sheet 2 /0/ F/q 4. H O` I INvEmUR .94mm 1; Procron BY @um 7L MATTORNEYS.

Patented ocr. 1s, 193s UNITED STATES PATENT OFFICE SOUND RECORDING AND-REPRODUCING MECHANISM Application March 26, 1936, Serial No. 70,962

21 Claims.

This invention relates to sound-recording and reproducing mechanism;especially to a head in which a stylus is adapted to be moved over therecord for recording or for playing the record,

5 and more particularly to a head of the so-called piezo-electric typein which movement of a crys'- tal device responsive to torsionalstresses set up therein by electrical current impulses or vibratorychanges originating in an electrical circuit modulated by the sounds tobe recorded are translated by the stylus into record track deformationsthe amplitude of which corresponds to the amplitude of the currentimpulses.

An important object of the invention is to l5 provide a head of thistype with crystal clamping means of such a novel character that when thecrystal has been fully clamped and without any current on it, thecrystal is at a position of no strain, so that when current is appliedit Will f respond with maximum effect and to an equal degree in eachdirection.

Such equality cannot be secured in cases Where' such a head by meansthat exert thereon a yieldn ing clamping pressure which may be regulated.in an exact manner to permit the crystal to respond with maximumeiiiciency to the electric impulses passing through the crystal alongits principal electrical axis, having regard both to the type ofmaterial tc be deformed and the pressure it is necessary to exertthereon. The crystal is also permitted by the yielding clamp to expandand contract in response to temperature changes.

All told, three adjustments of the crystal are provided for by thepresent invention; the first being that described in the foregoingparagraph at one end of the crystal; another adjustment at the other endof the crystal; and a third adjustment which permits the differences ofthe two ends of the crystal to be adjusted to each other so that whenthe crystal is not subjected to current it will be firmly clamped ateach end and there will be no strain internally.

In pursuance of the foregoing objects the invention includes means forimproving the stylus holder and in general the parts associated with thefree or active end of the crystal, such improved stylus-holding meanscomprising a split magnesium clamping member embracing the free edge ofthe laminated crystal slab across its breadth, and provided with a pivotring solidly embedded in the material of the clamp. A pair of screwsenable the operator to apply pressure upon the crystal, of an ordersuitable to permit expansion, but suilicient to avoid lost motion.

A cognate object of the invention is to provide a metal head of morethan ordinary Weight so that by affording a substantial base to thestylus, the vibrations of the latter will be translated into the desiredsound-track deformations and not dissipated in trepidation of theholder, and so absorbed uselessly.

A similar object is to provide exceptionally rigid, rm means to hold thestylus against any Wabbling movements, and thus to obviate a source ofdefect in the fidelity of recording and reproduction which hascharacterized similar structures in the art.

An object of the invention is to provide a recorder head with a novelmounting for the crystal and stylus so constructed that the stylus maybe used effectively to deform a material of high specic resistance todeformation, and consequently this resistance to formation of the soundtrack may be availed of to exert part of the damping effect requisite tochange the natural vibration amplitude of the crystal device and itsassociated parts, eliminating it as a source of defects in the record.

Other provision against vibration takes the form of a spring-biasedplunger engaged with the pivot oi the crystal device; and damping plugsare engaged between the clamp of the stylus holder and the main holderof the recording head. Means are provided to vary the tension upon theseplugs, which serve as auxiliary damping means to correct partially thefrequency peaks that are caused by the mass and Weight of the crystaldevice and its associated parts. It will be understood that the naturalperiod is a function that has many variable iactors such for example asthe size and weight of the crystal and associated parts.

It is intended that as between damping by the plugs and by the recordmaterial the resistance of the record material to deformation shall beutilized to effect part of the requisite damping effect, incontradistinction to the virtually entire absence of damping effect whenwax has been used for record material. The plugs may be relied upon formost or all of the remaining of the damping to be effected, Where aresistant record material such as aluminum is used, but

ltiti Cil if wax be used the plugs would have to be adjusted to effectthe amount of damping required.

A further object of the invention is to provide electrical lter circuitsto supplement the mechanical damping means in order to obtain thedesired recording response.

Still another object is to provide an acoustic blanket for the crystaldevice adapted to shield the same against extraneous sound vibrations ofan order capable of causing the crystal to vibrate on an undesiredfrequency; and as a means to further a similar object the faces of themetal casing may be loaded to render them nonresilient.

Other objects and features of the invention will appear as thedescription of the particular physical embodiment of the inventionselected for illustration progresses.

In the accompanying drawings, like characters of reference are appliedto corresponding parts throughout the several views comprised in thedrawings, in which:

Fig. 1 is a view in vertical longitudinal section of a recording head inthe construction of which the present invention has been embodied;

Fig. 2 is a view in horizontal sectional plan, taken on the line 2-2 o fFig. 1, looking upward;

Fig. 3 is a view in rear elevation, i. e., looking from right to left,of the main holder and associated parts shown in Fig. l, with the'casing omitted;

Fig. 4 is a fragmentary, detail view in vertical transverse section onthe line 4-4 of Fig. 1;

Fig. 5 is a similar view on the line 5-5 of Fig. 1 looking intheopposite direction;

Fig. 6 is a diagrammatic view of, a typical electrical circuit in whichthe crystal device of the present disclosure may be illustrativelyincluded; and a filter network is also shown.

In a now-preferred embodiment of the invention selected for illustrationand description, the part designated by the reference character H is abody member which may be designated as the main holder of the recordinghead, as distinguished from the stylus-holder" 2, in which a stylus S ismounted and caused to travel, by conventional or other suitable means,across a record blank R of suitable material which, in the presentinstance is preferably a metal such as aluminum or electrolyticallydeposited tin on a steel plate, or which may be cellulose acetate orwax.

The activating means for the stylus includes a crystal device of knownor other suitable form, designated generally by the reference characterC, and which is, in the instance illustrated, a laminated, slab-likestructure comprising a pair of elements c', c, made of compactedcrystalline components such as Rochelle salts having metal foil coatingsc over each outer face and between their adjacent faces, the elementsbeing assembled in known broadside juxtaposition. While the presentapplication shows such a laminated vcrystal of the twister type, it isto be noted that a single crystal may be used; also that the use of abender type of crystal is contemplated, with suitable modifications, i.e., a crystal bending longitudinal axes, crystals of both of these typesbeing known in this art.

The holder H is preferably made in part at least of metal of substantialweight, and comprises an upper part N from which extends upwardly a lugi shown as of a form conventional in the supporting arms for suchrecording heads; ill is an insulating plate, and below the plate aiaasssextends a block Il carrying a yielding clamping means I5 in which isfixed firmly, but with adjusted pressure, the adjacent end of thecrystal device.

The clamping means comprises a member preferably made of sheet-metal orother suitably rigid material, having an upright I6 secured to the blocki4, as by screws I1, and bent to form a stirrup i8 having a stud I9fitted in orifices 20 in the elements 2| of a leaf-spring 22, thisassembly being completed by an elongated top-plate 23 of invertedU-shape, which abuts against the inner margin of the lower face of thecrystal device C (see Fig. 1).

In the mounting of the crystal the left hand end, Fig. 1, is rst clampedin position. This causes the right end to assume a position at which thecrystal is not under stress. Then the screws 24 are screwed down untilthey just touch the upper side of the crystal. Then the screw |00 isadjusted causing the entire clamp to come up and compress the crystalagainst the screws 24 through the intermediate agency of the leaf spring22. The pressure on the crystal must not be too great because theemciency of the crystal is diminished under too great a pressure. Theproper pressure under which the crystal gives greatest response may bedetermined by the use of suitable known electrical measuringinstruments.

A cushion 9, of felt or other elastic `material, is interposed betweenthe ends of the crystal elements c, c and the upright I6.

Electrical terminals 26 and 21 are attached to the insulating upperplate I0, where they are provided with binding posts 28 and 29; theterminal 26 taking the form of a metal strap having ngers 30, 3|contacting respectively with the upper and lower foil facings c of thecrystal element, while the strap 21 is inserted between the crystalelements and contacts with the metal foil c therebetween, as at 32.

The reference character B designates an acoustic blanket of rubber orother suitable sounddeadening material by which the crystal elements areenveloped, and which is eiective against the propagation thereto ofsound vibrations of undesired frequency, and to prevent the crystal fromtransmitting soundy vibrations through the air and thus permitting feedback of the sound to the microphone and other instrumentalities. Itserves also as a protection against moisture.

The free ends c3, c4, of the crystal elements, in pursuance of theinvention, are embraced within a clamping member 33 preferablymagnesium,

occupying a medial slot 34 in the rear face of this clamp, which formspreferably an integral part of a one-piece device having the contour ofa very broad T. A layer of paper 34m may desirably be provided betweenthe crystals and the walls of slot 3d, and the edges of the slot may beof arcuate shape to make it more resilient and to compensate fortemperature changing eiects of the clamp, and the crystal. The shank i2of this member has already been referred to as constituting the holderfor the stylus, and it will now be seen that the stylus is mountedwithin a socket i5 having a double bore, one axis I 03 of which (see thedotted line position |02 of the stylus) is inclined at an angle of about2 to 5 to the vertical. This position is used for cutting wax or othermaterial, and for deforming records of aluminum or like materials theangle may be of the order of about 19. The bore of` socket 45 in whichthe stylus S is shown in full lines is proaisaaasvided to permit suchdisposition, the set screw 4I being effective' against the stylus ineach of the selected positions. This is about the same angle as that ofthe reproducing stylus employed in playing a record, and the dispositionof the recording stylus at this angle makes possible a more faithfulrecording in the record, by lreason of such ycorrespondence to theplaying position.

This disposition is a novel feature of the present invention, and isstressed at this point in the description for the reason that theresistanceof the record material is overcome in the present instance bythe exertion of unusual power supplied by the torsion of the crystaldevice C. The ability to deliver this requisite power with desirableelusitivity to the modulations of sound to be recorded, is dependent inlarge degree upon the improvements now to be described in the mountingof the clamping member 33 intermediate the crystal and the point ofpivot connection P in the front of the main holder.

For this purpose, each upper end part of the clamp 33, as 3B, 31, issplit, as at 38, and a pair of draft screws 39 serve to compress thesesplit ends upon the crystal with adjusted firmness, designed to securemaximum efficiency in operation of the stylus. A pivot ring 4|! isembedded in the material of the clamp and the pivot P extends throughthe pivot ring and through the contiguous wall h of the main holder H,which has an orifice h to receive the pivot. In order to prevent anyrattling of the pivot, a plunger 4i is provided in a bore 42 in the wallh in position to fit over the'upper rounded side of the pivot, and aspring 43, urges the plunger 4I against the pivot. A screw 44 serves tomaintain the tension on the spring.

At 46 I have shown a set screw, threaded into a bore 48 in the part l2of the stylus-holder, and this screw may be set up by a screw driverinserted through the orifice 48' in the front wall h of main holder' H.

Above the clamp portions 36, 31, a pair of elastic damping plugs 49 areinterposed, being set in sockets 50, and set screws i are provided toregulate the pressure of these damping plugs 49 against thestylus-holder. As hereinbefore explained these plugs are designed toexert a damping effect which may be subsidiary when the material of therecord to Ybe deformed possesses suitable resistance; or if therecording head is working upon a low-resistance material such as wax,the plugs 49 may constitute the principal damping medium.

It is to be noted that there can be no sidewise wobbling of the stylus,in View of the firm character of all the elements entering into itssupport, so that the recording or playing is exceptionally faithful.

Preferably the recording head will be formed with a metal casing 55surrounding four sides of the main holder leaving the front wall hexposed, while the top is covered by the plate insulating I0. This is a.convenient mode of construction, and facilitates removal of the casingat will to expose the parts mounted on the main holder and associatedwith the crystal. The casing may desirably have a lining 54 ofsound-absorbent material.

The typical circuit diagram illustrated in Fig. 6 will be understoodreadily by those skilled in the art of wiring piezo-electric crystalinstrumentalities.v In this figure the crystal device appears at C, and26 is the terminal connected with the exterior faces of the crystal, 21designating the terminal connected with the medial axis thereof.

Conductors II and 5l lead respectively therefrom to movable points onthe secondary il of an' equalizing coupling device E whose primary 59 isenergized by current supplied through conductors 60, 6i from anamplifier A. The latter derives current impulses through suitableconnections (not shown) from a source thereof modu' lated by the soundsto be recorded.

The reference characters 62, I3, C4, 0I, OO, Il indicate elements of alter net of well-known .form designed preferably to dampen out etl'ectscausedby mechanical vibrations rather than by electrical constants ofthe circuit.

At lill in Fig. 1, I have shown a spark-gap of known construction whichbridges the terminals 28-29, and may be adjusted to protect the crystalfrom unusual surges of.current or voltage which might tend to injure thecrytsal in the absence of such protection.

As an example of a modification which may be adopted without departingfrom the idea of means underlying the invention disclosed herein, acrystal device may be used for so-called hill-and dale recording inwhich the crystal is secured at three of its corners in a mannerconformable to the present invention, the stylus-holder being mounted atthe free corner of the crystal.

I have described what I believe to be the best embodiments of myinvention. I do not wish, however, to be confined to the embodimentsshown, but what I desire to cover by Letters Patent is set forth in theappended claims.

I claim:

1. A crystal device and support therefor to cooperate with a stylus inthe head of a mechanism of the class described, said crystal devicecomprising a crystal slab; means to impress thereon electrical currentsmodulated by ,the sounds to be transmitted so that said crystal devicewiil respond to the torsional effects thereby caused, a pivoted styluscarrier clamped to the crystal and capable of determining a normalposition for the crystal when the stylus is in a neutral position, andclamping means engaging and supporting the crystal at a distance fromthe stylus, comprising a rigid clamping member adjustable intoengagement with one side of the crystal in said normal position, and ayielding clamping member adjustable against the opposite side of thecrystal in opposition to the first clamping member, said clampingmembers kbeing symmetrically disposed with reference to the pivot of thestylus carrier, the construction and arrangement beingl such when thecrystal has been fully clamped and without any current on it. thecrystal is at a position of no strain, and when current is applied thecrystal will respond with maximum effect and to an equal degree in eachdirection.

2. In a recording head for a mechanism of the class described; a crystaldevice as claimed in claim i, characterized by an extended crystal slab;and further characterized by means for supporting one end of said slabrigidly against current-induced torsion; means for clamping the otherend of said slab with adjusted firmness to a stylus; and a means tocompensate adjustively for differences of the two ends of the crystal,so that when the crystal is not subjected to current, it will be underno strain internally substantially as described.

3. A crystal device for operating a recording instrument in the recorderhead of a sound-recording mechanism of the class described, said crystaldevice comprising a set of crystal components, means clamping thecrystal device crossvice and pivotally mounted to rock about an axis insubstantial alignment with the axis of the crystal, the construction andarrangement being such that said recorder-head may be used effectivelyto deform a material of high specic resistance to deformation wherebysaid resistance may be,

availed of to exert a substantial portion of the damping eiect requisiteto dampen the natural vibration amplitude of the crystal device and itsassociated parts substantiallyas described.

4. A recording head for sound-recording mechanism of the classdescribed, comprising a crystal device including a slab composed of acompacted aggregate of crystalline components, having at one end meansby which that end exclusively of the crystal device is clamped undercompression withcomplete rigidity against current-induced torsion. I

5. A recording head for sound-recording mechanism of the classdescribed, which includes a crystal device comprising a laminated slabcomposed of a compacted aggregate of crystalline components, having atone end means by which the crystal device can be yieldingly supportedwith adjusted rigidity and having a free end provided with means toclamp with adjusted firmness a'stylus adapted to translate intorecordtrack-deformation the movements of the crystal impressed upon thestylus as the crystal responds to torsional stresses set up therein byelectrical current impulses or vibratory changes originating in anelectrical circuit modulated by the sounds to be recorded.

6. A recorder head of the class described, including a crystal deviceprovided at a free portion with a stylus-holder and a main holdersupporting a clamp in which said crystal device is xed with completerigidity against current-induced torsion at the end' thereof remote fromsaid stylus-holder, said clamp being characterized by a means, such asleaf-springs, for transmitting the clamping pressure to the crystaldevice in a manner responding only to temperature-andmoisture-inducedexpansion effects; also by means to control the tension of said springs.

7. A recording head for sound-recording mechanism of the classdescribed, comprising a crystal device having means to support one endwith adjusted firmness and having mounted on its other end astylus-holder provided with a pivot, said head being furthercharacterized by a main holder on which said adjustable holding means ismounted, and also by a pivot associated xedly with said stylus holderand engaged pivotally in said main holder.

8. A recording head for sound-recording mechanism of the classdescribed, comprising a crystal device having means to support one endwith adjusted rmness and having mounted on its other end a stylus-holderprovided with a pivot, said head being further characterized by a mainholder on which said adjustable holding means is mounted, and also by apivot associated xedly with said stylus holder and engaged pivotally insaid main holder, also by a spring-biased means carried by saidmain-,holder and engaged yieldingly with said pivot to prevent rattlingthereof.

aisasss 9. A recorder head of the class describedf'including a crystaldevice, a clamping means in which one end of said crystal device is heldwith complete rigidity against current-induced torsion, a stylus-holderon the remote end of said crystal, the latter being responsive freely tocurrent-induced torsion, and a main holder for said crystal and itsassociated parts.

10. A recorder head of the class described comprising the crystaldevice, clamping means, stylus-holder, and main holder elements,combined and cooperating as set forth in claim 6,`

comprising a crystal device responsive to soundinitiated modulations inan electrical circuit, a lter circuit adapted to dampen out eiectscaused by mechanical vibrations rather than by electrical constants ofthe circuit.

l2. In a recording head of the class described, a main holder, a crystaldevice supported rigidly against current-induced torsion exclusively atone end, by clamping means thereon, yand an acoustic blanket envelopingsaid crystal dvice and eiective against the propagation thereto of soundvibrations of undesired frequency, and also against emission of soundfrom the crystal.

13. In a recording head of the class described, a main holder, a crystaldevice supported rigidly against current-induced torsion exclusively atone end, by clamping means thereon, and a metal casing surrounding saidmain holder and crystal and having sheet metal faces loaded to quenchsound vibrations.

14. A stylus-holder adapted to embrace one edge of a laminated crystaldevice, in a recording head of the piezo-electric type, saidstylus-holder comprising a generally T-shaped body having a socket inwhich said stylus may be supported adjustively at an angle of about 19to the record upon which said stylus is to operate, and at an angle morenearly approaching the perpendicular.

l5. A stylus-holder in a head of the class described, comprising agenerally T-shaped body, and further characterized by having a slot eX-tending medially along the head of said T, and by having theend-portions of the T slotted to form spaced clamping means for the edgeof a crystal lying in said medial slot, and tension bolts to-apply saidsplit portions to said crystal with adjusted pressure.

16. In a recording head of the class described, an assembly comprising amain holding means, a crystal device made of laminated components, and ametal clamping means at each end of said crystal device, each clampingmeans having at least one ply of sheet insulating material intermediateit and the crystal, means to hold said crystal at one end of said mainholder by a pivotal extension of said clamp at that end, and means tohold said clamping means xedly with yielding firmness in the clamp atthe other end of the crystal.

17. A recording head for sound-recording mechanism of the classdescribed, in which a cutter-head is adapted to be moved transversely ofthe record, and which includes a crystal device comprising a (ctile slabor) mass composed of a current impulses or vibratory changesoriginataing in an electrical circuit modulatedby the sounds to berecorded, said recording head being characterized by a conformation suchthat its principal electrical axis extends through the center of thecrystal, also by electrical terminals so disposed as to supplyelectrical current to iiow through the crystal from one face at rightangles i to the axis of the other face, so that the crystal' in responseto such changing current impulses causes vibration of the stylus varyingin ampli- .tude according to the amplitude of the current impulses.

18. In a piezo-electric apparatus, the combl-V nation of a Rochelle saltmultiple-plate piezoelectric unit adapted in operation toilextorsionally, a case enclosing the unit, means operatively supporting theunit in the case, and a rotatable spindle attached to the unit with theaxis of the spindle in line with the torsional o! the unit..

said spindle being mounted in a wall section of the case.

19. In a piezo-electric apparatus, in combination, a piezo-electriccrystal unit adapted in operation to ex torsionally. means supportingone end of the unit in fixed position, a spindle connected with thecrystal unit at the opposite end thereof. and means rotatably supportingthe spindle in line with the torsional axis oi' the unit.

20.'In a piezo-electric apparatus, in combination, a piezo-electriccrystal unit adapted in operation to ilex torsionally, means supportingone end of the unit in xed position, a spindle connected with thecrystal unit at the opposite end thereof. means rotatably supporting thespindle in line with the vtorsional axis of the unit, and a styluscarrier ailixed to said spindle for oscillation in unison therewith.

2l. In a piezo-electric apparatus, in'oombination, a piezo-electriccrystal unit adapted in operation to iiex torsionally` means supportingone end of the unit in fixed position, a spindle connected with thecrystal unit at the oppomte end thereof, means rotatably supporting thespindle in line with' the torsional axis of the unit.

and an oscillatory member affixed to said spindle for oscillation inunison therewith.

BARTON A. PROCDOR.

